Installing Clang for QDoc

QDoc uses Clang when parsing C++ files as well as function signatures in \fn commands. Clang is part of the LLVM Compiler Infrastructure Project. If you're going to build QDoc from source, you must install Clang 17.0 or later.

Installation Options

Qt's Prebuilt Packages (Recommended)

Qt provides officially supported prebuilt LLVM/Clang packages that are tested and used for Qt's official builds:

• Download from: https://download.qt.io/development_releases/prebuilt/libclang/qt/.
• Available for Windows, macOS, and Linux.
• Support static linking of LLVM/Clang libraries.
• Version alignment with QDoc requirements and Qt’s CI.

System Package Managers

As an alternative to Qt's prebuilt packages, you can install Clang through system package managers. QDoc specifically needs the Clang compiler libraries and their CMake configuration files. The dependencies are:

• llvm-<version> (infrastructure)
• clang-<version> (compiler and libraries)
• libclang-<version>-dev (development headers)
• libclang-cpp<version>-dev (C++ API development files)

The following lists some typical invocations of package managers on popular Linux distributions and macOS.

Linux

LLVM and Clang are separate packages in most distributions. Ensure you install the (versioned) -dev packages that provide the file ClangConfig.cmake.

• Debian/Ubuntu: apt install libclang-dev clang libclang-cpp-dev
• Fedora/RHEL: dnf install clang-devel
• Arch Linux: pacman -S clang llvm

macOS

Use Homebrew's llvm formula:

• brew install llvm
• For ARM64 Macs: Configure with LLVM_INSTALL_DIR="/opt/homebrew/opt/llvm"
• For Intel Macs: Configure with LLVM_INSTALL_DIR="/usr/local/opt/llvm"

Configuration

When Qt's configure script cannot locate LLVM/Clang libraries, it will display platform-specific installation guidance and the exact configuration commands needed for your system.

To manually specify a custom LLVM installation location:

• Set the LLVM_INSTALL_DIR variable: configure LLVM_INSTALL_DIR="/path/to/llvm" FEATURE_clang=ON
• Or add to CMAKE_PREFIX_PATH: configure CMAKE_PREFIX_PATH="/path/to/llvm" FEATURE_clang=ON

After installing LLVM/Clang libraries, always reconfigure with FEATURE_clang=ON to enable QDoc compilation.